NMR or MRI
In Magnetic Resonance Imaging (MRI) systems and nuclear magnetic resonance (NMR) systems, a static magnetic field (B) is applied to the body under investigation. The magnetic field defines an equilibrium axis of magnetic alignment in the region of the body under investigation. An RF field is applied in the region being examined in a direction orthogonal to the static field direction, to excite magnetic resonance in the region, and resulting RF signals are detected and processed. Generally, the resulting RF signals are detected by RF coil arrangements placed close to the body. See for example, U.S. Pat. No. 4,411,270 to Damadian and U.S. Pat. No. 4,793,356 to Misic et al. Typically, these coils are either surface type or volume type coils, depending on the application, and are used to transmit RF and receive NMR signals from the region of interest (ROI).
A further increase in signal to noise ratio (S/N) can be realized with the use of quadrature coils (as opposed to the conventional linear coil design). See for example U.S. Pat. No. 4,467,282 to Siebold and U.S. Pat. No. 4,707,664 to Fehn. Also, for highly homogeneous and quadrature volume coils (commonly referred to as the birdcage and the transverse electromagnetic (TEM) wave resonators, respectively), see U.S. Pat. No. 4,783,641 to Hayes, U.S. Pat. No. 4,751,464 to Bridges, and U.S. Pat. No. 6,029,082 to Srinivasan et al..
Birdcage Coil
The birdcage coil is well known in the art and includes two end rings connected by several straight segments, which are referred to as legs. The birdcage coil has several resonance modes, of interest being the principal k=1 mode for homogeneous imaging. The principal mode has two linear modes, oriented orthogonal to one another. The outputs from these modes can be combined using analog circuitry or digitally combined in a receiver system. The birdcage coil provides about a 41% improvement in S/N and expends about one-half of the power of a conventional linear coil.
In addition, owing to the sinusoidal currents in the coil periphery, the birdcage coil provides a highly homogeneous B field in the transverse planes (XY) inside the coil, which is ideal for imaging (e.g., whole-body, head, knee, wrist, etc. for adults). The B field profile along the coil axis, however, mimics a Gaussian distribution with a maximum at the coil center.
The B field distribution is improved over the adult head with an end-capped design disclosed by Hayes (see, e.g., Book of Abstracts, p 39-40, 5th ISMRM, 1986). The end-capped design provides a more uniform distribution toward the top of the head. At the open end along the coil axis, the B field distribution for the end-capped coil design falls off like a conventional birdcage, which is ideal for imaging the adult head.
Neonate Incubator
Incubators are commonly used in hospitals in the neonatal intensive care units (NICUs) as life sustaining devices for the ill neonate. These incubators help to maintain the micro-environment of the ill neonate with high levels of temperature (up to 39 deg C.), humidity (up to 100%) and oxygen (up to 100%) prescribed by the doctor and required by the patient. Generally, mildly ill neonates are transported to the magnetic resonance (MR) scanner and placed inside the super cooled MR system for diagnosis. No effort is made to maintain the micro-environment surrounding the patient to the original NICU conditions inside the incubator. This is due to the unavailability of an incubator system that is MRI compatible.
Recently, a submission was made to the European Patent Office (see EP 01 109 195.6, filed Apr. 12, 2001 and PCT Application WO 02-083053A1, filed Apr. 12, 2001) by Lonekker-Lammers et al. (Lonekker) for an incubator/transporter system that is MRI compatible. With the MRCI of Lonekker, safe transport is possible between the NICU and the MRI sections. Further, the neonate is left untouched inside the incubator when scanned inside the MRI system. Once the MRI scan is complete, the patient is transported back to the NICU in the same incubator system. Thus, the incubator settings (e.g., temperature, humidity, oxygen) are not altered and the environment of the neonate is not disturbed.
In summary, the Lonekker MRCI performs similar to the conventional NICU transport incubator with the added feature of MRI compatibility. The added feature provides the clinicians the necessary diagnostic information which may lead to prompt clinical/pharmacological/surgical interventions, which in turn can save precious lives.
MRI is a diverse imaging tool commonly used in the diagnosis/prognosis of illnesses in the pediatric population. MRI diagnosis, however, depends on image quality. For a particular field strength, high image qualities over the ROI can be achieved with a high S/N RF coil.
At present, neonates are imaged using adult coils inside the super cooled MR scanner without the incubator. Should the incubator be used inside the MR scanner, the S/N of the MRI experiment will greatly suffer due to the larger adult size coils, which encompass the incubator. Specialty RF coils must be used to attain optimum S/N and imaging resolution. Further, the coils must withstand the harsh environment (high temperature, high levels of humidity and oxygen) within the incubator. In addition, the design must allow rapid positioning/removal over the patient pre/post MR scan and must allow placement of endo-tracheal tubes (ett) and similar devices (e.g., ventilator tubes) attached to the patient.
By using a coil within the incubator, high image S/N and thereby high image quality can be realized in reasonable scan times. With the improved S/N, one can increase the imaging resolution or reduce the scan time, thereby reducing patient risks while concomitantly increasing throughput in an MR scanner.
A whole body RF coil was designed by Dumoulin et al. for a prototype incubator (see Dumoulin et al “A Self-contained neonate incubator for use with MR scanners” in Proc. ISMRM Scientific Meeting, 10 (2002), p 2558, Abstract). Dumoulin's coil is large and is used to scan the brain and torso of the neonate. The coil has 8 legs that extend out radially to connect to the end rings. Since this coil has a large volume, low filling factors are realized, which can result in non-optimum S/N over the imaging volume.
Accordingly, there is a need in the art for an RF coil that can be used with an MRCI that provides optimum S/N and imaging resolution. In addition, it would be advantageous for the coil design to allow rapid positioning/removal over the patient pre/post MR scan and to allow placement of endo-tracheal tubes (ett) and similar devices (e.g., ventilator tubes) attached to the patient. Further, it would be advantageous for the coil to withstand the harsh environment commonly found in an incubator (e.g., high temperature, high levels of humidity and oxygen).
The present invention is intended to enhance the S/N of the MRI RF coil system over pre-, term- and post-term pediatric head and body (age 0-3 months). In addition, the present invention is intended for use within the MR compatible incubator (MRCI) without significantly sacrificing its performance or the performance of the incubator.